The present invention relates to a method and a system for detecting different characteristics indicative of a desired property of a sample, and in particular to a method and a system for voltammetric characterization of a liquid sample.
In WO 99/13325 there is disclosed a method for detecting different characteristics indicative of a desired property of a sample, such as the concentration of an analyte, pH etc. Said method is based on voltage pulses according to a pulse-sequence comprising a plurality of pulses in sequence and at different amplitudes, being applied to electrodes. The obtained response signals are used as input to a pattern recognition program in a computer for interpretation and for outputting results. The analysis is based on multivariate methods, such as PCA (Principal Component Analysis). A brief account of PCA is given in an article by F. Winquist et al in xe2x80x9cAn electronic tongue based on voltammetryxe2x80x9d, Analytica Chimica Acta, 357 (1997) 21-31. This article and the WO publication are both incorporated herein in their entirety by reference.
The above method is essentially characterized by.
Use of pulse voltammetry (or other electrical measurement methods) to obtain information (transient curves);
Use of different electrode materials, modified electrodes or pulse-sequences etc. to induce different chemical reactions so as to vary the transients;
Use of curve fitting methods to extract or sample information from the obtained set of transients;
Use of various multivariate signal-processing methods to interpret the information gained thereby.
Particularly, said method teaches that only or mainly the first part of the response transient is measured and used. Thereby, a very rapid testing or tasting can be carried out since the first part of the transient is of a very short duration. With the first part is here meant the initial rising slope up to the peak.
In EP application number: 00128297.9 (hereafter referred to as EP ""297) the applicants disclose an ozone sensor based on the ideas of WO 99/13325. It is shown in EP ""297 that satisfying results concerning detection of ozone may be achieved by performing pulsed voltammetric measurements using a single working electrode of Rh. But it is further shown that the overall performance of a four-electrode sensor is better than a sensor with a single electrode of Rh. Therefore, the preferred embodiment of this novel ozone sensor is a sensor device with a multiple working-electrode arrangement, wherein each working electrode is made of a different material than the others. The EP ""297 publication is incorporated herein in its entirety by reference.
However, the pulse-sequences for voltammetric measurements shown both in WO 99/13325 and EP ""297 involve many pulse-steps and are therefore time consuming, especially if multi-electrode arrangements are used, whereby each pulse-sequence have to be repeated for each electrode.
The object of the invention is to provide a new method for voltammetric characterization of a liquid sample and a system for voltammetric characterization, which method and system overcomes one or more drawbacks of the prior art. This is achieved by the method for voltammetric characterization of a liquid sample, using a voltammetric setup comprising at least two working electrodes and a counter electrode that are placed in contact with the liquid sample, the method comprising the steps of: a. applying a first potential on all working-electrodes, b. performing a number of voltammetric cycles according to a predetermined pulse-sequence, each comprising the steps of: i. applying a second potential on the counter electrode according to the pulse-sequence, ii. performing a predetermined number of measurement procedures, each comprising the steps of: removing said applied first potential from all but one of the working electrodes, registering the current passing through the working electrode still having said first potential applied thereto, storing the registered value in a data storage unit, applying the first potential on all working electrodes, and c. analyzing said stored values using a predetermined mathematical model to produce a result.
There is also provided a system for voltammetric characterization, comprising: at least two working electrodes, a working electrode selecting unit enabling connection and disconnection of one or more of the working electrodes to a first potential, a counter electrode connected to a second potential, a current registration unit, arranged to register the current passed through the working electrode(s) connected to said first potential, a control unit arranged to control said second potential, said working electrode selecting unit and to read current values from said current registration unit at predetermined points in time, a data storage unit for storing said current values, and a processing unit arranged to analyze the stored current values using a predetermined mathematical model, and to output the result from the analysis.
One advantage with such a method and system is that the time needed for the voltammetric detections is reduced to a great extent.
Another advantage is that the system may be produced as an integrated device, thus providing a fully functional, compact system at a low cost.
Embodiments of the invention are defined in the dependent claims.